The present invention relates to measurement devices. More specifically, the present invention relates to a hand held measuring instrument, such as a compass, used to measure scaled or unscaled distances on a surface.
A wide variety of measurement device are known in the art. Examples of simple measurement devices include rulers and tape measures. More complex devices include rulers with sliding or rotating position indicators. Also known are compasses and calipers having mechanical or electronic displays. Examples of a variety of measurement devices are described in U.S. Pat. Nos. 2,557,428, 3,113,381, 4,270,273, 4,388,759, 4,612,656, 4,839,833, 4,915,112, 4,941,267, and 5,327,907, each of which are wholly incorporated herein by reference. Other devices include rolling measurement devices used to trace an arc or a convoluted boundary.
However, these measurement devices fail to provide a simple, yet highly accurate measurement device for use in applications where measurements are based on a printed scale and where a high degree of precision is required. These applications include taking measurements on a variety of medical scans, such as X-ray films, radiographs, computed tomography (CT), magnetic resonance (MR), ultrasound nuclear medicine and the like. Similar measurement devices are required in other medical applications, such as medical physics and cardiology where the measurement of heart rates and timing of events in the cardiac cycle are necessary. Non-medical applications often require accurate measurements on scaled medium. These include, for example, architectural or engineering drawings, aeronautical and nautical navigation charts, and clothing pattern designs.
More specifically, the prior art measurement devices suffer from one or more of the following disadvantages. Most of the prior art devices have a design that is unfamiliar to the average user and, therefore, require a learning process to be used properly. Many require two hands to use. Most only work well when placed on a planar surface, rather than in situations where a linear measurement in three dimensional space is needed. Other designs, such as rolling measurement devices, do not trace straight lines well and can only approximate linear distances. Other designs have structural features that block the user""s view of the item measured, the boundary of the item or the area surrounding the measured item.
The present invention overcomes these disadvantages by providing a measurement device having a pair of legs. Each leg has a measurement point and a fulcrum end, the fulcrum ends providing a pivot point for the legs so that the measurement points arcuately move apart from one another. The measurement device has a transducer assembly connected to at least one of the legs which measures leg displacement and generates a distance signal. The measurement device has a programmable processing unit adapted to process the distance signal and display a distance measurement on an electronic display.